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Pathogenicity and whole-genome analysis of a Siniperca chuatsi-derived Nocardia seriolae strain
Liting Chen1,2, Xin Yan1,2, Yongju Luo1,2
1Guangxi Key Laboratory of Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Academy of Fishery Science, Nanning, Guangxi, China.
Insights
A novel bacterial strain identified as Nocardia seriolae caused high mortality in Siniperca chuatsi. This study details its genomic, pathogenic, and antibiotic resistance profiles for disease control.
Area of Science:
- Aquatic animal pathology
- Bacterial genomics
- Fish disease research
Background:
- Diseased Siniperca chuatsi (mandarin fish) in Guangxi, China, exhibited mortality since 2023.
- A bacterial strain, designated 20230510, was isolated from affected fish kidneys.
Purpose of the Study:
- To identify and characterize the bacterial pathogen responsible for Siniperca chuatsi mortality.
- To investigate the virulence, genomic features, and antibiotic susceptibility of the isolated strain.
Main Methods:
- Isolation and artificial infection of bacterial strain 20230510.
- Morphological, pathological, whole-genome sequencing (WGS), and antibiotic susceptibility analyses.
- Phylogenomic analysis for strain identification and virulence gene identification.
Main Results:
- Strain 20230510 caused 100% mortality in S. chuatsi, with a low LD50, confirming high virulence.
- WGS identified a large genome and 403 potential virulence genes. Phylogenomics confirmed the strain as Nocardia seriolae.
- Histopathology revealed granulomatous lesions, primarily in kidneys, and identified antibiotic resistance genes.
Conclusions:
- Nocardia seriolae strain 20230510 is the causative agent of disease and mortality in S. chuatsi.
- Genomic and virulence data provide insights for developing effective disease control strategies.
- Antibiotic susceptibility testing identified effective treatments, including enrofloxacin and doxycycline.
Abstract:
A bacterial strain (No. 20230510) was isolated from the kidneys of diseased Siniperca chuatsi in Guangxi, China, since 2023. Artificial infection experiments demonstrated that this strain caused the observed disease in S. chuatsi. The isolate underwent morphological, pathological, genomic (whole-genome sequencing, WGS), and antibiotic susceptibility analyses. Infection trials revealed 100% mortality in high-concentration groups, with an LD50 of 3.89 × 104 CFU/mL, indicating high virulence. WGS results showed a circular chromosome of 8,123,106 bp (GC content: 68.14%), containing 7,638 CDSs, 72 tRNAs, and 12 rRNAs. Phylogenomic analysis revealed that strain 20230510 (CP130742) clusters with three N. seriolae strains with 98% bootstrap supporting, confirming its identification as N. seriolae. Further analysis identified 403 potential virulence genes linked to nutrient metabolism, regulatory factors, immune modulation, effector delivery systems, and exotoxins. Chromosomal comparisons also detected multiple antibiotic resistance genes. Susceptibility testing confirmed sensitivity to nine antibiotics, including enrofloxacin, doxycycline, florfenicol, and sulfamethoxazole. Histopathology revealed chronic granulomatous lesions, most severe in the kidneys, with similar but milder damage in the liver, spleen, gills, and intestines. These results confirm N. seriolae strain 20230510 as the pathogenic agent behind S. chuatsi mortality, offering key insights for developing control strategies.
